Photograph courtesy NASA Earth Observatory
Volcanoes are awesome manifestations of the fiery power contained deep within the Earth. These formations are essentially vents on the Earth's surface where molten rock, debris, and gases from the planet's interior are emitted.
When thick magma and large amounts of gas build up under the surface, eruptions can be explosive, expelling lava, rocks and ash into the air. Less gas and more viscous magma usually mean a less dramatic eruption, often causing streams of lava to ooze from the vent.
The mountain-like mounds that we associate with volcanoes are what remain after the material spewed during eruptions has collected and hardened around the vent. This can happen over a period of weeks or many millions of years.
A large eruption can be extremely dangerous for people living near a volcano. Flows of searing lava, which can reach 2,000 degrees Fahrenheit (1,250 degrees Celsius) or more, can be released, burning everything in its path, including whole towns. Boulders of hardening lava can rain down on villages. Mud flows from rapidly melting snow can strip mountains and valleys bare and bury towns. Ash and toxic gases can cause lung damage and other problems, particularly for infants and the elderly. Scientists estimate that more than 260,000 people have died in the past 300 years from volcanic eruptions and their aftermath.
Volcanoes tend to exist along the edges between tectonic plates, massive rock slabs that make up Earth's surface. About 90 percent of all volcanoes exist within the Ring of Fire along the edges of the Pacific Ocean.
About 1,900 volcanoes on Earth are considered active, meaning they show some level of activity and are likely to explode again. Many other volcanoes are dormant, showing no current signs of exploding but likely to become active at some point in the future. Others are considered extinct.
More About Volcanoes
-
Deep Sea Vents: Science at the Extreme
Peer into the sunless world of the deep sea, where fantastic creatures thrive in a harsh environment believed until recently to be completely uninhabitable.
-
Photos: Indonesian Volcano Erupts
One of the word's most active volcanoes, Mount Merapi is the bringer of life and death for a wide swath of the island of Java.
-
Volcanoes Killed Off Neanderthals?
Eruptions may have wiped out our heavy-browed cousins, but we survived by being largely out of the line of fire, study suggests.
-
Photos: Volcano Consumes Home
As lava from the Kilauea volcano crept closer to his Hawaiian home, resident Gary Sleik felt three years of anxiety go up in smoke.
-
Electric Ash Found in Iceland Plume
Ash from the Eyjafjallajökull volcano was charged even over Europe—a find that's both good and bad news for air traffic, scientists say.
-
Mount St. Helens Before & After
From snow-capped peak to smoldering crater, see how the major eruption 30 years ago today changed the face of the famous volcano.
-
Ten Most Dangerous U.S. Volcanoes
Thirty years after its famous eruption, Mount St. Helens holds steady at number two. See the full list, ranked by government experts.
Photo Galleries
Video
The Green Guide
Shop National Geographic
Advertisement
Green Living Hot Topics
-
Organic Air Fresheners
Avoid toxic chemicals and create a calming space.
-
Surprising Recyclable Household Items
With a little know-how, you can recycle more than you think.
-
Side Effects of Vegetarianism
Find out how to stay healthy and eat lower on the food chain.
More on Japan's Earthquake and the Pacific Ocean Tsunami
-
Tsunami-Debris Cruise Announced
Tourists are paying thousands to sail through a floating field of debris from the Japanese tsunami that could be the size of California.
-
Photos: Cleanup at Fukushima
Radioactive decay, contaminated water, soil, and hot spots pose challenges for Japan after the nuclear accident at Fukushima.
-
Rare Video: Japan Tsunami
The March 11 earthquake and tsunami left more than 28,000 dead or missing. See incredible footage of the tsunami swamping cities and turning buildings into rubble. Video.
Special Ad Section
The World's Water
-
Visualizing Our Global Water Footprint
You might be surprised to see how the daily choices you make affect critical watersheds around the world.
-
Why Care About Water?
National Geographic's freshwater initiative is a global effort to inspire communities to conserve water and restore rivers.
National Geographic Magazine
-
Photos: In the Field
Browse breathtaking images of life on the Serengeti.
-
A Thing or Two About Twins
Can the unique bond between identical twins be explained?
-
Visions of Earth
Browse stunning images of our planet as seen through a photographer's eye.

